The Moving Velocity of Cumulus Humilis Clouds

Abstract

The horizontal movement of cumulus humilis clouds near Sapporo was measured by the stereophotogrammetric method in the summer seasons of the years 1969 to 1971 in Sapporo. The direction and speed of individual cloud movements were presented on charts. The environmental meteorological conditions were obtained from the Sapporo rawinsonde soundings. By comparing the analytical results of clouds with the environmental meteorological conditions, the following results were obtained. The direction of horizontal movement of the higher cumulus humilis clouds was nearly the same as that of prevailing wind direction at the cloud level (exactly speaking, near cloud base level), however, the direction of the lower clouds was not in agreement with the wind direction. The critical ground height for the agreement of cloud motion direction with wind direction was found to be about 700 meters. The speed of horizontal movement of cumulus humilis clouds was generally less than prevailing wind speed at the level of cloud base. It was also found that the speed of larger clouds was slower than that of the smaller clouds when their heights were the same. The general tendency was that the lower the clouds, the lower the motion speeds, and the greater the vertical wind shear, the lower the cloud speed. The slowness of cloud speed was qualitatively explained by considering the upward transportation of low horizontal momentum in thermal convections under a condition of the positive vertical wind shear.

Motion of echo structures observed with volume imaging atmospheric radar

“…9 includes results from Table 1 of Chiyu et al (1973), on motion of shallow cumulus clouds above land near Sapporo (43.11N, 141.41E)-27 measurements from stereo photographs, on 12 summer and autumn mornings, compared to the wind vector from radiosondes a few km away. Maximum cloud and wind speeds from Chiyu et al are lower as measurements are up to 1.5 km above ground.…”

“…However, thermals can move at a different speed from the background wind, retaining their horizontal momentum while rising through wind shear (Chiyu et al, 1973;Kuettner et al, 1987). Shiino and Aoyagi (1981) report active convection moving at $0:35 or less of the background wind speed.…”

Lenticular wave cloud above the convective boundary layer of the Rocky Mountains

“…2(b) and (c) cannot persist for several hours in the absence of any forcing (Lou and Teitelbaum 1993). However, strong shear across continuous convective updraughts above the mountain summits at 1200 LT would be consistent with a convection wave (Kuetmer et al 1987;Bradbury 1990;Chiyu et al 1973). The peaks of the Rocky Mountains are regions of enhanced convection, for instance spawning thunderstorms (Banta and Schaaf 1987).…”

A Laboratory Experiment of Thermals with Generation of Heat

“…Cumulus clouds were also measured in their early stage in Sapporo (Chiyu et al 1973). Froude number were calculated for small cumulus clouds.…”